Drawbead structures are used to control the flow of the sheet metal blank into a drawing die. Generally, known drawbead structures include a male drawbead structure or semi-cylindrical bead on the face of one die binder and a groove or female drawbead structure in the face of the opposing or other die binder. The drawbead structure is located outside the trim line of the drawn part since the edge portion of the sheet metal blank which passes through the drawbead structure is deformed and must be trimmed off.
The restraining force of such known drawbead structures results from a combination of deformation forces and friction forces. The deformation forces occur from the bending and straightening of the edge portion of the sheet metal blank as it passes around the radiused portion of the bead and the radiused shoulders of the groove. The friction forces occur from the rubbing contact of the sheet metal with the aforenoted radiused bead portion and shoulders. Generally 75% of the restraining force is due to deformation forces and 25% is due to friction forces.
Drawbead structures are conventionally built on and into the die during die tryout and the restraining force is set by adding material to the bead or groove, such as by welding, or removing material therefrom such as by grinding, in a trial and error manner. This is time consuming and expensive and is done manually.